Various display devices have been developed as image display devices of light weight and small thickness. Main categories of such image display devices include, for example, image display devices using light emitting diodes (LEDs), liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs) and the like. An LED display formed by arranging light emitting diodes, in particular, can be used by itself as an image display device, and can also be used as a backlight for a liquid crystal display device.
For full-color LED displays in which light emitting elements emitting colors different from each other are arranged and made to emit light sequentially to display a full-color image, in particular, various techniques for arranging the light emitting elements, light emission procedures and the like are known.
For example, Japanese Patent Laid-Open No. Hei 9-198007 discloses a display device formed such that the numbers of red light emitting pixels, green light emitting pixels, and blue light emitting pixels arranged in a form of a matrix are in a ratio of 1:2:1.
According to Japanese Patent Laid-Open No. Hei 11-133887, pixels are formed such that each pixel has one red sub-pixel, one green sub-pixel, and one blue sub-pixel disposed therein. Specifically, a technique is disclosed in which one pixel is formed by sub-pixels R and G arranged along a first scan electrode, a sub-pixel R arranged along a second scan electrode, and sub-pixels G and B arranged along a third scan electrode, thereby reducing a pixel pitch as compared with a case where three sub-pixels R, G, and B are arranged in one line, and correspondingly increasing display density. Also, a technique is disclosed which makes time-division display by a combination of illumination/non-illumination of these sub-pixels and thereby makes multiple-color display.
In an in-line type image display device where a red sub-pixel emitting a red color, a green sub-pixel emitting a green color, and a blue sub-pixel emitting a blue color are arranged in order in a horizontal direction and sub-pixels arranged in the same pattern as the pattern arranged in the horizontal direction are arranged at equal intervals in a vertical direction, each pixel is formed so as to include one sub-pixel emitting the red color, one sub-pixel emitting the green color, and one sub-pixel emitting the blue color. Hence, pixels are formed as RGB units by the same arrangement of sub-pixels in the horizontal direction, and sub-pixels emitting the same color are arranged in the same column in the vertical direction. By thus arranging sub-pixels and making each of the sub-pixels emit light by time division, an image is displayed. At this time, sub-pixels emitting the same color and arranged in the same column are illuminated, and columns of sub-pixels are illuminated sequentially, whereby the image display can be made.
Conventionally, pixels are formed such that one pixel separately includes one red sub-pixel, one green sub-pixel, and one blue sub-pixel. Therefore, the number of sub-pixels needs to be three times the number of pixels or more, and an image display device in which light emitting elements serving as light sources of an LED display are arranged has a large number of light emitting elements forming sub-pixels. Further, for size reduction and resolution improvement of the image display device, it is important to reduce distance between pixels and arrange light emitting elements at a high density. It has also become important to reduce the number of parts without degrading picture quality as well as reduce the size of the light emitting elements. In addition, in an image display device formed by arranging a large number of light emitting elements at a high density, there may be a case where not all light emitting elements are driven normally. Thus, it is also important to drive light emitting elements with a high reliability and thereby make high-quality image display.
In the meantime, depending on a position of a sub-pixel formed by a light emitting element of a high visibility, the conventional arrangement of sub-pixels may cause a difference between a desired display position of a pixel and a position of the pixel actually perceived by the eye of a person viewing the image.
With decrease in the size of light emitting elements, the number of light emitting elements arranged on a screen is increased. Therefore, the image display device is generally constructed by forming sub-pixels on unit panels, and arranging a plurality of these unit panels in a form of a matrix on a device substrate. In this case, at an edge portion of a unit panel, a part for connection with the substrate of the image display device or the like is required, and hence a certain region having no elements arranged therein is required. It is also important to secure a region for compensating for variations in size of the unit panels and size resulting from thermal expansion. In addition, there is a desire for techniques for easily manufacturing a high-quality image display device by efficiently arranging light emitting elements.
Accordingly, in view of the above problems, it is an object of the present invention to provide an image display device that makes it possible to form pixels with a smaller number of sub-pixels as compared with a case where one pixel is formed so as to separately include one each of sub-pixels of three colors of R, G, and B, and which can make full-color display by making the sub-pixels emit light by time division. It is another object of the present invention to provide an image display device that can secure a region with no light emitting elements arranged therein at an edge of a unit panel without degrading picture quality by thinning out sub-pixels at the edge of the unit panel. It is a further object of the present invention to provide a method of manufacturing an image display device which method makes it possible to manufacture the image display device efficiently.